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The Diaphone Fog Signal

Diaphones were a once familiar sound heard throughout the Great Lakes from the early 1920s until the late 1960s / early 1970s when most lighthouses were automated. 120 such installations existed on both U.S. and Canadian waterways in the 1950s. The two most commonly heard Diaphones were the “Standard” Diaphone, which gave a full steady upper tone that terminated in a heavy “grunt” tone, and the classic two-tone Diaphone that produced an upper tone followed by a full steady low tone of equal or greater duration than the upper tone.

Robert Hope-Jones

In 1895, Robert Hope-Jones, an English pipe organ designer and builder, developed a special tone generator for his famous WURLITZER organ; the WURLITZER was a popular musical instrument in the days of silent movies and live stage performances. The new tone generator consisted of a casing that contained a slotted cylinder with a similarly slotted piston. Air was channeled through the casing in such a way that it caused the piston to reciprocate within the cylinder. The major portion of the air was discharged through the slots in both the piston and cylinder as the piston stroked back and forth in the cylinder. As the air passed through slots in the piston, it was “chopped” which caused a vibration that was amplified though a long cone shaped trumpet. Hope-Jones labeled this new tone “diaphonic” (meaning two or more tones”). The new tone had a full, powerful harmonic structure that could be heard over some of the other tones on the pipe organ. He called his new tone generator a Diaphone.

Diaphones x2 - photo Jeff Laser

Around 1900, John Pell Northey, a machinist / inventor who owned a factory that made valves and pipe fittings, met with Robert Hope-Jones soon after Hope-Jones moved to the United States. John Pell Northey took an interest in Hope-Jones’s invention and after some negotiating, obtained the rights to patent the Diaphone. Northey immediately redesigned the Diaphone so that a secondary air supply could be directed to the cylinder, which would give the piston a more vigorous and uniform means of reciprocating within the cylinder. Northey called this modification to the casing the “motor” section (or chamber). By increasing the overall size of the instrument and adding his motor air chamber, John Pell Northey had developed an extremely powerful, harmonically rich sound signal that would soon become the greatest foghorn ever produced. In 1903, Northey patented his improvements to Robert Hope-Jones’s invention and formed his DIAPHONE SIGNAL Co. COY LTD. (also known the CANADIAN SIGNAL Co.) at Toronto, Ontario, Canada. The first Diaphone employed as a foghorn in the U.S. was at Buffalo, N.Y. in 1914. Diaphones ranged in size and function from the tiny single tone Type “A” to the “Standard” units (Types “C-C” through the huge Type “L”) which produced a high tone that terminated in a heavy descending “grunt” tone, to the classic two-tone Type “F-2-T” foghorn.

Standby diaphone - photo Jeff Laser

The Type “F” unit was the most commonly employed Diaphone worldwide. The sound of the Type “F” Diaphone is produced by low-pressure air (35 – 40 pounds per square inch) being introduced to the piston and cylinder through the motor and speaking chambers of the Diaphone’s casing. The main air supply to a typical Type “F” Diaphone is through 4″ pipe to the speaking chamber and 1- ½” pipe to the motor chamber. At some point near the Diaphone, the 4″ pipe is reduced down to 1- ½” pipe. The 1-½” air supply to the motor chamber is controlled by a 1-½” air actuated operating valve called the motor valve. The motor valve usually has a threaded input and a flanged output. The motor valve also has a ¼” inlet at the bottom of the valve body, and a ¼” outlet between the valve body and the output flange. The ¼” inlet is from a timer that activates a pilot valve (usually a solenoid of some type) which in turn activates the motor valve.

“Speaking” air is the air supply that actually flows through the slots in the piston and cylinder and creates the tones of the Diaphone. The Speaking valve is configured similarly to the motor valve but it is much larger (4″) and has no ¼” outlet near its output flange.

Air compressor - photo Jeff Laser

The operation of the “Standard” Diaphone is as follows: Until the timer (or code machine) opens the pilot valve, the control air supply to both operating (motor and speaking) valves, and the air supply to both the motor and speaking functions is restrained behind each valve respectively. When the timer activates the pilot valve, control air passes along the control air tubing to the ¼” inlet in the bottom of the motor valve. The control air lifts a piston in the lower chamber of the valve body which in turn lifts a valve stem / valve disk assembly. As the valve disk lifts from its seat, the full force of the motor air supply is allowed to pass through the valve to the motor chamber of the Diaphone. Some of the motor air is diverted through the ¼” outlet at the output side of the motor valve. The diverted motor air travels down a short length of tubing to the ¼” inlet in the bottom cover of the speaking valve and lifts the piston / valve stem / valve disk assembly in the speaking valve. As the speaking valve opens, the main charge of speaking air flows into the speaking chamber of the Diaphone. Almost instantly and, simultaneously, the motor air causes the piston to reciprocate in the cylinder as speaking air is forced between the slots in both the cylinder and piston. The combination of the action of the motor air and speaking air creates a high tone of

Another compressor - photo Jeff Laser

approximately 250Hz. (Hertz, or cycles per second). When the Diaphone timer closes the pilot valve, the flow of control air to the motor valve ceases and the motor valve closes. The closing of the motor valve causes an interruption of the flow of motor air to the motor air chamber as well as the flow of control air to the speaking valve. There is some “lag” in the closing of the operating valves. The motor valve closes first, which causes the Diaphone piston to begin to slow down. Due to the lag between the closing of the valves, a final puff of reduced pressure speaking air is forced through the slots in the less rapidly reciprocating piston. This action creates a tone of much lower frequency than the high tone (somewhere between 93 – 150 Hz.). This brief low tone is referred to as the “grunt” tone in “Standard” operation of the Diaphone. Mariners could sometimes hear the grunt tone when the high tone was “masked” by other sounds or the vessel was at a great enough distance from the foghorn that the high tone would be inaudible anyway (low frequency sounds carry farther, in air than high frequency sounds).

Compressor and piping to tank - photo Jeff Laser

Around 1929, John Pell Northey’s son Rodney redesigned the Type “F” Diaphone so that the normal grunt tone could be extended to produce a full steady sustained low tone of equal or greater duration than the high tone. This modification to the Type “F” Diaphone proved so effective that it was used to replace the larger Type “G” and Type “K” units in the U.S. (only 1 Type “K” Diaphone was ever employed in the U.S. and that location was on the Farallon Islands off the coast of California) and became the standard for all new major installations. Rodney called his new revision the “Improved” Type “F” Diaphone. In fact, some of the early issues of this unit have simply TYPE “F” DIAPHONE nameplates.

Gas powered air compressors - photo Minnesota Historical Society

By 1932 Rodney Northey had inherited the DIAPHONE SIGNAL Co. from his father. Due to the effects of the Great Depression on the Canadian economy, Rodney was forced to sell the company in order to stay financially “afloat” and marry his fiancé. Most of the patent rights, foundry patterns, blueprints, and machining tools were obtained by DECK BROTHERS – PRECISION MACHINISTS of Buffalo, New York under contract by, and for, the U.S. Government (more specifically the U.S. Lighthouse Service). After this transaction occurred, the name of the Improved Type “F” Diaphone was “Americanized” and changed to Type “F-2-T” Diaphone.

Twin resonators - photo Terry Pepper

The “F” in “F-2-T” means that the Diaphone is essentially a Type “F” Diaphone [the diameter of the piston in both units is approx. 5″ and both units employ the same size of resonator (trumpet) and operating valves]. “2-T” means that the unit produces a true two-tone signal where the low tone is a sustained tone instead of a “grunt”. “F-2-T” Diaphones were more commonly heard on the west coast and frequently used on lightships on U.S. waterways. Recordings of these two-tone foghorns can be heard in old cartoons, old radio and television shows (i.e.; the door bell on the ADDAMS FAMILY), old movies, and even a soap commercial that exclaimed that their product prevented “BEEEE-ooooh”. A nice feature of the “F-2-T” Diaphone is that it can be configured to operate as a “Standard” Type “F” Diaphone.